1996 polaris slt780

hi i am having some trouble with my skis i have two matching slt 780s and have loved them but i have lost compression in one of them and two of my pistons are marked up and one of them is messed up the pistons say 78a 0.50 on the top of them. I am having trouble finding pistons and what else do i need to fix it. Can anybody help me with my problem i would surely appreciate any advice or if you have any parts i would be interested in buying them. Thanks alot for any help